This invention relates to an apparatus and method for unloading powder from a drum shaped shipping container. More specifically, the invention covers an apparatus and method for unloading powder coating material from a rotating drum shaped shipping container.
In electrostatic finishing with a powder coating material, the powder is typically delivered to a spray gun from a hopper. For example, the powder can be transferred from a shipping drum to a hopper associated with a powder spray system, as disclosed in U.S. Pat. No. 4,505,623, assigned to Nordson Corporation, the assignee of this invention. The 4,505,623 patent, which is hereby incorporated by reference in its entirety, shows and describes the withdrawal of the powder from a shipping drum being supported with its axis at a 45 degree angle to vertical. The powder is then transferred to a feed hopper and pumped from the feed hopper to a spray gun for application to a substrate.
Various difficulties have been experienced in transferring the shipping powder from the drum. For example, the powder is often compacted during shipping and cannot be mixed with the air to fluidize the powder and enhance discharge. This problem is more pronounced with certain difficult to handle powders, such as acrylic based powders, or powders which have relatively smaller particle size distribution. The latter powders are particularly difficult to fluidize. In some cases the shipping drum is vibrated to loosen the powder. However, as the powder is evacuated from the drum, the vibration tends to compact the material and form a solid arch about the evacuated area around the inlet opening of the suction tube which draws the powder from the shipping drum. Then, the operator must manually free the powder and direct it toward the suction tube, or alternatively, the suction tube must be moved to the location of the powder. Thus, even though the vibrating device, as shown in the 4,505,623 patent, is intended as an automatic transport device, it sometimes must be manned by an operator to ensure that substantially all of the powder is removed from the container.